1. Field of the Invention
The present invention relates to the marking of gambling chips having the general shape of a disc, or of objects of similar shape, by pad printing. Gambling chip, also called casino chip, should be understood to mean any element which can be used in gambling halls and represents a nominal value which may or may not be predetermined. Generally, these chips are manufactured from a rigid and scratch-resistant plastic.
2. Discussion of Background Information
Gambling chips are, almost systematically, given a decoration by marking on their faces and/or sides, this decoration, depending on the eventual uses of the chips, possibly ranging from the simplest to the most complex. For the rest of the specification, the term decoration should be understood in its widest sense and it comprises, in particular, any drawing, symbol, mark and character (for example, letters, numbers, bar codes or various codings) capable of graphical representation and/or having a visual or optical effect (for example, by the use of U.V. -sensitive ink). More specifically, the decoration of the chips is capable of fulfilling at least one of the several functions presented briefly below:
i) a chip and/or chip value and/or casino and/or gambling table and/or gambler identification function;
ii) a decoration function, the decoration having an aesthetic aspect and/or acting as an advertising medium; and
iii) a chip-authentication and security function, for combatting the risk of falsification and/or the risk of fraudulent reproduction.
Patent FR 2,730,392 in the name of the Applicant describes the use of pad printing for marking the surface of the faces and/or side of chips (as opposed to volume marking using multi-shot injection molding of variously colored plastics). In particular, this patent describes the marking of each face of the chip by pad printing using an inked pad which is moved coaxially with the chip with, for chips having a soft-profiled side without a straight side, marking of part of the side corresponding to the chamfered or rounded edge of the face of the chip. However, this technique, although satisfactory for the faces of the chip, is not always accepted by casinos for the side as it results in substantial modification of the profile of the side and/or in incomplete marking of the latter.
Moreover, again according to Patent FR 2,730,392, side marking for straight-sided chips is carried out by lateral marking using a rotating pad (or a rotating pad/roller for marking several stacked chips simultaneously). However, this technique, whose means of implementation are quite complex and expensive, is not always satisfactory, especially when the side decoration has to be reproduced with very great positional accuracy over the entire circular perimeter of the straight side (writing, bar code and various codings, periodic circular drawing). In particular, since the principle of the rotating roller implies a point of origin on the side of the chip for the marking operation proper, this results in the formation of a xe2x80x9cjoinxe2x80x9d (either a blank or an overlap) in the decoration after marking the side over one complete revolution of the chip, the xe2x80x9cjoinxe2x80x9d being all the more difficult to avoid as the manufacturing tolerances of the chip cause slight, but quite real, variations in the diameter of the chips.
The invention recognizes that there is a need for a new method of marking straight-sided gambling chips which eliminates, or appreciably reduces, the limitations and other drawbacks presented above.
For this purpose, the invention provides a method of marking the side of a straight-sided disc-shaped gambling chip or an object of similar shape by pad printing, characterized by the use of an inked pad which is moved coaxially with the chip in conjunction with a flat ink plate having a ring-shaped zone suitable for being placed coaxially with the pad and bearing a decoration image defined by a radially deformed representation of the decoration of the straight side of the chip.
Thus, the use of the decoration image which is radially deformed with respect to the side decoration makes it possible to distribute the effect of distortion on the final decoration due to the variations in diameter of the chip over the entire circumferential perimeter of the side of the chip and to make this effect negligible.
According to a first variant of the invention, the decoration image is obtained by the combination of an operation of radially folding up the decoration for the side of the chip around a facial edge included in the plane of the ink plate and of an operation of contracting the decoration towards the facial edge, the sequential or chronological order in which the two operations are performed being of no consequence,
In particular, according to a first way of implementing the method of the invention, the decoration image is obtained from an intermediate decoration produced by radially folding up the side decoration into a reference plane corresponding to the plane of the ink plate and including one of the faces of the chip (the reference face), by way of a radial transformation of contraction of the intermediate decoration in the reference plane towards the center of the ring bearing the decoration image.
Advantageously, the position of the internal circular border of the ring and the contraction coefficient of the radial transformation are determined, for a given straight-sided chip model and a given pad, by marking the chip model using a positioning ink plate set on the axis of the chip and bearing a pattern consisting of closely-spaced concentric circles.
Most advantageously, the characteristics of the radial contraction transformation are chosen in order to obtain a reduction in the radial height of the intermediate decoration (equal in height to the side decoration) of between 25 and 40%, i.e. a radial contraction coefficient of between 0.75 and 0.6.
In practice, the magnitude of the radial contraction and of the associated reduction in height of the side decoration depend on the deformation of the pad on the surface of the chip, in other words they depend on the type of chip to be marked, on the profile and nature of the pad (material, hardness, surface finish) and, to a lesser extent, on the inks employed.
Moreover, in order to solve the problem of the colours of the decoration marked on the side of the chip lightening due to the inked pad stretching, use is made, according to two variants of the invention, either of an ink plate having a halftone decoration image for a face of the chip and a non-halftone side decoration image or an ink plate having a decoration image for a face of the chip and a deeply-etched side decoration image, the etching of the side decoration image then being deeper than the etching of the decoration image for the face of the chip.
Moreover, by making the internal circular border of the ring come into correspondence with the edge of the reference face of the chip, the heightwise positioning of the decoration is facilitated for marking a solid-straight-sided chip. Likewise, it is advantageous, in the radial contraction transformation, to use as relative origin on each radius OR the corresponding point A on the edge of the reference face of the chip.
It should be pointed out that the invention also applies to soft-edged chips having a central straight side extending substantially over a large portion of the thickness of the chip and connected to the two faces of the latter by two transition zones (small fillets or broadened chamfers).
According to another variant of the invention, these central-straight-sided chips are marked by making the internal circular border of the ring to correspond approximately to the circle of axial projection of the straight side on the reference face of the chip.
According to yet another variant of the method according to the invention, an axially symmetric deformable pad is used which has a diameter at least equal to the diameter of the chip increased by about five times the height of the side of the chip.
Apart from the chips and other straight-sided objects of similar shape, the straight side of which is pad-printed using the method of the invention defined above, the invention also relates to a pad-printing device suitable for implementing this method, which includes a support for the chip, the support being equipped with a mechanism for centering the chip coaxially with the pad before the operation of marking the side by pad printing, the centering mechanism being retractable in order to allow the side of the chip to be marked during movement of the pad.
Advantageously, the retractable centering mechanisms, of the type comprising slides or a centering ring, are mounted so as to slide axially over the perimeter of the support.
Most advantageously, the device accordingly to the invention includes a mechanism for holding the chip in place on its support, especially when raising the pad. In particular, the mechanism for holding the chip in place includes at least one adhesive patch, in contact with that face of the chip which bears on the support, and/or of suction under vacuum.
Other characteristics and advantages of the present invention will appear on reading the description which follows, with reference to the drawings appended hereto.